Palicourea Aubl. includes in its traditional sense about 250 species of shrubs and small trees distributed widely in the New World tropics. Palicourea plants are typically found in the understory and subcanopy of moist to wet tropical forests, from low to high elevations. As traditionally recognized,
Palicourea has flowers with well developed tubes that are odorless, mostly brightly colored, and assumed to be pollinated by hummingbirds, and the genus has been diagnosed by these flower characters; in particular it was separated from Psychotria, which shares general flower and fruit form but was identified by its usually white, smaller, insect-pollinated flowers. In this traditional circumscription Palicourea has been studied primarily regionally (Steyermark 1972, 1974; Bacigalupo 1952; Burger & Taylor 1993; Jung-Mendaçolli et al 2007; Taylor 1989, 1993, 2000, Taylor et al. 2007), and a synoptic overview has been presented (Taylor, 1997).
However, morphological (Taylor, 1996) and molecular studies (Nepokroeff et al., 1999; Andersson, 2001; Andersson & Rova, 1999; Sedio et al., 2013) have found that the flower characters that were used to separate traditional Palicourea from Psychotria, are more variable than were noted, and are widely homoplasious and variable within the overall lineages that can be identified. Thus "traditional" Palicourea includes species that are closely related to many neotropical species classified in Psychotria subg. Heteropsychotria Steyerm. (Steyermark, 1972), and Palicourea plus many of the species of Psychotria Subg. Heteropsychotria together comprise a single monophyletic group that is diagnosed by stipule and fruit characters. This expanded or combined group takes the name Palicourea, and has sometimes been referred to as "Palicourea sensu lato". This group also includes many of the species formerly included in Cephaelis. Cephaelis was also diagnosed by inflorescence characters, specifically having the flowers all grouped in a single head that is enclosed by well developed involucrate bracts, and that inflorescence arrangement has also arisen in parallel multiple times within this single monophyletic group. Thus it now appears that inflorescence and corolla characters are widely variable within this group and represent pollinator adaptation by individual species, with both hummingbird pollination and capitate inflorescences with involucral bracts evolving several times within this group (Nepokroeff et al., 1999; Andersson, 2001; Andersson & Rova, 1999).
Palicourea in its new or current, broadened circumscription has stipules that are bilobed and persistent, at least on the nodes near the stem apex; terminal inflorescences with determinate axes; generally five-merous flowers with bilocular ovaries; fleshy drupaceous fruits that become blue, purple-black, or occasionally white at maturity; and pyrenes generally with marginal preformed germination slits and a groove on the adaxial face, and without an alcohol-soluble red pigment. Psychotria s. str. or "true" Psychotria is also found in the Neotropics, and differs from Palicourea in its stipules that are generally quickly deciduous and have a line of persistent (though often small) colleters that remains on the stem at the stipule insertion portion; fruits that are orange or red at maturity; and pyrenes that are flat on the adaxial face and lack pre-formed germination slits but have an alcohol-soluble red pigment. The form of Palicourea's stipules varies widely but they are bilobed at least weakly (Taylor et al., 2016) and this separates this genus from the similar Neotropical genus Rudgea. Some species that have been included in Psychotria subg. Heteropsychotria however do not belong to Palicourea, and have been separated into other genera based on morphological and molecular characters, in particular Carapichea, Coccochondra,
Transfer of the remaining species from Psychotria subg. Heteropsychotria to Palicourea is underway; the list of species of Palicourea below includes all the species that have been formally transferred to this genus, and the placement in the infrageneric classification of Palicourea is noted on each species's page.
Palicourea in its current, broader circumscription is estimated to include about 600-800 species, though new species are numerous and continue to be discovered at a fairly constant rate so the final number is difficult to estimate. This group has extensive homoplasy in reproductive characters, as demonstrated by the molecular phylogenetic analyses, and not surprisingly vegetative characters also vary. Traditional Palicourea was reviewed by Taylor (1997) who presented an infrageneric classification. However Neotropical Psychotria has never been reviewed as a whole so the merging of these two groups into an expanded Palicourea requires study of the individual species of Psychotria. This work expands the infrageneric classification of Palicourea (Taylor et al. 2010; Taylor 2014, 2015, 2016). The majority of species currently treated in Palicourea belong to Subg. Montanae, but it apparently most of the species of Psychotria Subg. Heteropsychotria may belong to Subg. Palicoure and these two groups may actually be similar in number of species.
The stipules of Palicourea are characteristically united around the stem into a continuous sheath or have the intrapetiolar portion reduced, forming laminar or sub-interpetiolar stipules; in a few species the sheath is prolonged into a tube (Palicourea locellata, though this is not closed at the top to form a calyptrate stipule as in some species of Psychotria. The stipules range from emarginate or nearly truncate, to deeply lobed with the lobes short to very well developed; in some species the lobes are erose, fimbriate, or laciniate (e.g., Palicourea woronovii, Palicourea octocuspis). Palicourea was traditionally separated from Rudgea by its non-glandular stipules, while those of Rudgea had well developed glands on the lobes or adaxial part of the sheath; however a number of Palicourea species have well developed glands on the lobes and/or the abaxial part of the sheath (e.g., Palicourea sect. Nonatelia). The leaves vary from small to quite well developed (e.g., Palicourea grandifolia, Palicourea woronovii), and are generally opposite but sometimes verticillate (e.g., Palicourea corymbifera). The habit of the plants varies from small unbranched subshrubs (e.g., Palicourea cuspidulata), monopodial plants that accumulate detritus along the stems (Palicourea woronovii), or usually small to large shrubs or occasionally small trees; no annuals or climbers are yet known in this genus.
The inflorescences of Palicourea are terminal in position. However frequently the stem continues grown from one or both of the axillary buds that subtend the peduncle; when both buds develop the terminal position is clear, but when only one develops the position (or its terminology) has been confused. Here the inflorescences are considered terminal because they develop from the terminal bud of the stem. When the stem continues growth from one of the axillary buds, the inflorescences are subsequently displaced to an apparently axillary position, but in this case the inflorescence is solitary on the side and an undeveloped axillary bud can be located between the leaf and the inflorescence on that side, while the axillary bud on the other side has developed; these inflorescences are here considered pseudoaxillary (Robbrecht, 1988), and have been called by some authors also "lateral"; these inflorescences are considered developmentally terminal and distinct from axillary inflorecences that are formed by each of the axillary buds while the terminal bud continues to develop. The inflorescences of Palicourea vary widely in form, from lax and extensively branched with reduced bracts to subcapitate and densely congested ("capitate") with large showy bracts. Nearly all Palicourea species are distylous; this appears to be the ancestral condition for the genus, and it seems to have been lost in peripheral, isolated populations of some species (Sobrevila et al., 1983) and om some species on Caribbean islands (Taylor, 1993).
The diversity of species and morphology, and in particular inflorescence arrangement, flower features, and display colors, is stunning in Palicourea and exploration of montane areas of Central and South America continues to discover new, morphologically unexpected species at a significant rate. Understanding of the component species and their features will be necessary to understand the factors that have stimulated this exceptional diversification in Palicourea. The wide variation in inflorescence and flower features in the group, including the range of display colors, suggests that diversification is related in good part to pollination adaptations, as proposed for a diverse montane group of Solanaceae that grows together with Palicourea and has generally similar flowers, pollination, and variation (Muchhala et al., 2014). Palicourea also includes a good amount of variation in infructescence arrangement and color, fruit size and color, and pyrene form, so adaptations for dispersal also probably play a role. As with any study of evoluationary patterns, a solid and reasonably comprehensive taxonomy of the study group is needed before its radiation can be accurately understood. This taxonomy is the current focus of my work.
Author: C.M. Taylor.
The content of this web page was last revised on 4 August 2016.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml